1. Field of the Invention
The present invention relates to a device for utilizing electron beams, and more particularly relates to electron interference technologies used in interference electron microscopes and others.
2. Description of the Related Art
An electron interference device pertains to a technique for quantitatively measuring an electromagnetic field in a substance or in a vacuum by measuring a change in phase of an electron beam. FIG. 1A, illustrates an interference optical system in an existing electron holography. An electron beam 2 which has been emitted from an electron source 1 goes forward as illustrated in the drawing. A current density of the electron beam is adjusted by a first illumination electron lens 3 and a second illumination electron lens 4, a sample 6 is disposed on one side of an optical axis between the second illumination electron lens 4 and an objective lens 5, and the sample 6 which is placed on a parabolic surface 42 of the objective lens 5 is irradiated with the electron beam. An image obtained by an action of the objective lens 5 is magnified by a magnifying lens 9, an electron beam 7 which has passed through a first region (the sample) on the parabolic surface 42 and an electron beam 8 which has passed through a second area on the parabolic surface 42 are bent inward by a second electron biprism 10 and are superposed on an observation surface 11 and interfere with each other, and thereby interference fringes are detected. A phase is recovered from the obtained interference fringes and the change in phase of the electron beam caused by the presence of the sample 6 is obtained.
An electron biprism has a function of deflecting electron beams passing along the right and left sides of a filament electrode which is disposed between parallel plates disposed in parallel with a traveling direction of the electron beam inward or outward relative to an optical axis with an electric field which is generated between the filament electrode and the parallel plates by applying a potential to the filament electrode. In general, a system having a mechanism which rotates relative to the optical axis and a system having a mechanism for moving an electron biprism within a plane vertical to the optical axis are commercially available. Incidentally, in this specification, although when the electron biprism strictly indicates a filament electrode in an optical system, it will be expressed as the “filament electrode of the electron biprism” or the “filament electrode”, and when it is used customarily as an electron beam deflector, it will be expressed simply as the “electron biprism”, with respect to numerals to be assigned to respective elements, numerals which are the same as the above will be used.
In the above-mentioned method, the electron beam 7 passing through the first region and the electron beam 8 passing through the second region are adjacent to each other at the position of the sample 6. A width of an interference region which is measured in conversion of the sample surface is limited by a coherence length in a sample in-plane direction of the electron beam which has been radiated to the sample surface (see Tonomura A., (1987) Applications of electron holography, Rev. Mod. Phys. 59: pp. 639-669). In addition, Japanese Patent Application Laid-Open No. 2006-216345, Japanese Patent Application Laid-Open No. 2006-164861, Japanese Patent Application Laid-Open No. 2006-313069, Japanese Patent Application Laid-Open No. 2011-249191, WO2010/026867 and Japanese Patent Application Laid-Open No. 2011-040217 are proposed as patent documents relating to such devices as mentioned above.